When driving a light emitting element (i.e., a current element) to be controlled by a supplied current, such as an organic EL or a light emitting diode, it is necessary to control a minute electric current supplied to the current element. Out of these, regarding the organic EL, with an increase in efficiency of the organic EL, it has been required to accurately and quickly control a minute current supplied to the organic EL especially in a hold mode.
On the one hand there has been a large demand for lower power consumption and the efficiency of an organic EL element is expected to continue increasing, on the other hand development of TFTs has been rapidly carried out to achieve a high mobility. However, a definite drive method has not been developed, and demands for a higher definition image and increase in the number of gray scales are expected to increase in the future.
FIG. 10 is a circuit diagram illustrating a conventional drive circuit shown in Patent Literature 1. According to the drive circuit of FIG. 10, a gate electrode of a transistor 10 is connected with a scanning line Xi and a drain electrode of the transistor 10 is connected with a drain electrode of a transistor 12. The drain electrode of the transistor 12 is connected with a power line Vi, and a gate electrode of the transistor 12 is connected with a source electrode of the transistor 10. A source electrode of the transistor 12 is connected with a drain electrode of a transistor 11 and with an anode of an organic EL element Ei,j. A gate electrode of the transistor 11 is connected with the scanning line Xi, and a source electrode of the transistor 11 is connected with a signal line Yj.
During a selection period, a power signal voltage, which is equal to or lower than a reference potential Vss, is applied to the power line Vi. When the scanning line Xi goes into an H (high) state during the selection period, the transistors 10 through 12 go into an ON state. Further, a voltage applied across the organic EL element Ei,j becomes zero or a reverse bias. Accordingly, a programmed sink current Ij passes in a direction indicated by an arrow α.
Since the transistor 12 goes into the ON state during the selection period, a gate-source voltage Vgs, which corresponds to drive performance of the transistor 12, is applied to a capacitor 13. This causes electric charge corresponding to the gate-source voltage Vgs to be stored in the capacitor 13.
After the end of the selection period, i.e., during a non-selection period during which the scanning line Xi is in an L (Low) state, a positive voltage is applied between the gate and source of the transistor 12 by the capacitor 13, which had been charged during the selection period. This causes only the transistor 12 to be in the ON state.
During the non-selection period, a power signal voltage applied to the power line Vi is a power supply voltage Vdd which is sufficiently higher than the reference potential Vss. Accordingly, a voltage, which is a forward bias, is applied to the organic EL element Ei,j, thereby allowing a constant current to pass through the organic EL element Ei,j.
Such a drive method is called a current programming method, which makes it possible to allow a constant current to pass through the organic EL element regardless of variation of TFTs of pixels.